README: refactor the filter module section and add a few notes
README: refactor the filter module section and add a few notes

Put the linear module up first as it's special, using the ts_calibrate
config file.

Then list the filters with full multitouch support and below put the filters
with issues last, mentioning their issue.

kergoth/tslib,kergoth/tslib,kergoth/tslib,kergoth/tslib